Octagen's long-term goal is to develop an essentially human, low immunogenicity form of recombinant factor VIII ("fVIIl") for patients with hemophilia A, a condition caused by a congenital absence or insufficiency of the clotting plasma protein fVIll. Hemophilia A is treated initially with replacement human fVIII, which can be either genetically engineered or derived from pooled plasma. However, approximately 25 percent of such hemophiliacs develop significant inhibitor antibodies to human fVlll, which seriously complicates management of the disorder. The overall aims of this project are to further assess in certain pre-clinical studies two putative low immunogenicity fVIII constructs earlier identified through a collaboration between Octagen and Emory University researcher John S. Lollar, as well as to evaluate additional closely related molecules. In particular, the specific aims of the project are to: 1. conduct a randomized trial of candidate low immunogenicity fVlll constructs in hemophilia A mice; 2. determine the dose-dependent immunogenicity of one of the two current candidates in hemophilia A mice (hereafter that candidate is referred to as "A2C2epi3"); 3. compare the clearance of A2C2epi3 and a "wild-type" recombinant human b domain deleted fVIII (hereafter referred to as "HSQ"); 4. compare the hemostatic efficacy of A2C2epi3 and HSQ in hemophilia A mice; 5. compare the binding of A2C2epi3 and HSQ to phospholipid; 6. compare the binding of A2C2epi3 and HSQ to human von Willebrand factor (vWf); and 7. optimize the expression of A2C2epi3 and a second earlier identified candidate in a baby hamster kidney-derived cell line designated BHK-M.